Drilling apparatus



May 12, 1953 J. F. JOY 2,638,325

DRILLING APPARATUS Filed Dec. 29, 1947 5 Sheets-Sheet l May 12, 1953 J. if. JOY

DRILLING APPARATUS 5 Sheets-Sheet 2 Filed Dec. 29, 1947 May 12, 1953 J. F. JOY l 2,638,325

DRILLING APPARATUS Filed Dec. 29, 1947 5 Sheets-Sheet 3 QMW,

zfarizey May 12, 1953 J. F. JOY. 2,638,325

DRILLING APPARATUS Filed Dec. 29, 1947 5 Sheets-Sheet 4 l :arm 9 I 5l 47 46 XV 45 I-l |Yr u Ihnen/far.'

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May 12, 1953 J. F. JOY 2,638,325

DRILLING APPARATUS Filed Dec. 29, 1947 I 5 sheets-sheet 5 151.1914" rrrl/07 IS7/venan' Patented May I2, 1953 UNITED STATES PATENT OFFICE DRILLING APPARATUS Joseph F. Joy, Pittsburgh, Pa., assigner to Joy Manufacturing Company, Pittsburgh, Pa., a corporation of Pennsylvania Application December 29, 1947, Serial No. 794,281

(Cl. Z55-39) Claims. l

This invention relates to drilling apparatus, and from one aspect thereof, to drilling apparatus by which a drilling implement may be rotated and caused to perform a boring operation and which also incorporates means for imparting to the rotating implement a rapid series of impacts and thereby greatly increasing the drilling speed. From another aspect, it relates to devices for iinparting a rapid series of blows to a drilling implement, regardless of Whether, as is very desirable in some forms of construction such as are hereinafter described, there be rotation of the implement to cause it to operate with a boring action, or whether the implement accomplish its drilling substantiallv wholly percussively, with rotation only tc effect presentation of the cutting edge or edges of the implement in various positions to the material being drilled, thereby to eicct more efficient operation.

Drilling devices for eecting the rformation of holes by a boring action are well known. Those of a type for forming holes by percussion are well known. So also are devices in which the material penetration is effected by peroussive actuation of a drill. bit, with rotation of the bit n between blows to effect change of its position relative to the material to be drilled, in order that such material may be more eiectively cut away. The present invention, from its aspect rst above mentioned, comprises means-improved in itself for superimposing upon a ooring action, for the effecting of which improved means is provided, a rapid impact action, which is transmitted through the implement to the material bein detached and, by the cutting action, deepened boring out, and the vibration. provides Aa very fast eiective formation and deepening oi `the hole. The invention also includes, from itsother aspect, and as a part of its rst aspect also, improved means for effecting the percussiv-e actuation of a drilling implement. In accordance with invention. from one aspect, a motor, preferably an electric motor, may drive the drillimplement for rapidly rotating the implement to e'ect boring, and this same motor may drive 'a mechanical impact mechanism which delivers a rapid series of impactblows to the drilling implement as the latter is rapidly rotated, to supplement the boring action with -an impact action to increase the drilling speed. rthere may oe associated with the impact and rotating mechanism, and likewise driven hy the motor, means for 'mechanically conveying the cuttings from the `drill hole as drilling progresses. Also, the 'motor has a novel cooling arrangement.

2 t is an object fof the present linvention to provide an improved drilling apparatus. Another object is to provide an improved drilling apparatus for drilling blast holes in coal or similar material whereby high speed penetration lof the material' is possible. A further object is to provide an vimproved rotary drilling apparatus having embodied `there-in improved means for imparting a vibratory Ior percussive action to the drilling implement to increase the drilling speed. Yet another object is to provide an improved impact mechanism for percussively actuating la drilling implement. Still another object is to provide an improved rotating .and impact mechanism for actuating a drilling implement and driven by a rotary motor such as an electric motor. Another object `is to provide improved drilling apparatus having novel arrangements and combinations .of parts. rI'hese `and other objects and advantages of the invention will, however, hereinafter more fully appear.

In lthe accompanying drawings there are shown vfor purposes of 'illustration two forms which the invention, in at least one of its aspects, may assume in practice.

In these drawings:

Fir. 1 is a, side elevational View, with parts shown in longitudinal ver-tical section, illustrating a drilling apparatus constructed in laccordance with a preferred illustrative embodiment -of the invention.

Fig. 2 is a rear end view, and Fig. 3 a front end view, both on a reduced scale, of the `drilling apparatus shown in Fig. l.

Fig. 4 is an enlarged fragmentary vsectional view illustrating the sealing means between -the conveyor tube and the walls of the vdrill hole.

Fig. 5 is an enlarged View in longitudinal vertical section taken substantially on line 5-5 of 2, land iifit'h the forward portion thereof `lirolren away.

Fig. 6 isan enlarged cross-sectional view taken substantially on line 6--6 of Figs. 1 and 5.

Fig. '7 is a fragmentary sectional view taken substantially lon line Fl-l of Figs. l and 5.

Figs. 8 and 9 are fragmentary sectional views, with parts shown in full, showing parts of the impact lmechanism in '-d-iierent operating posi- 'tions` Fig. 10 is a longitudinal vertical sectional view taken substantially on line lll-:I0 of Fig. 5, and with 'parts shown in full.

Figs. l1, v12 and 13 rare-detail views of the-:crank and arm `mechanism for :actuating the impact element, and with the parts shown in different operating positions.

Fig. 14 is a side elevational View of a drilling apparatus constructed in accordance with a modified embodiment of the invention from one of its aspects.

Figs. l and 16, when taken together, constitute a vertical sectional view through the drilling apparatus shown in Fig. 14..

Fig. 1'7 is a vertical sectional view taken substantially on line |l|| 'i of Fig. 15.

Figs. 18 and 19 are detail views showing the crank mechanism of Fig. 17 in different operating positions.

In both embodiments of the invention, the improved drilling apparatus is shown of the portable handheld type, although, evidently, features of the invention may be embodied in drills of other types.

The drilling apparatus shown in Figs. 1 to 13 inclusive is especially adapted for use in drilling coal or similar materials and is generally designated l, and generally comprises a casing or housing Z provided with a longitudinal supporting handle 3 and lateral supporting handles 5, 4 `and carrying a motor 5, preferably an electric motor, which actuates a drilling implement having a detachable drill bit 'l of a conventional design. The drilling implement is rotated through rotating mechanism 8 and percussively actuated is associated with the motor 5 for cooling the latter.

The casing or housing Z includes a central body portion i3 provided with a detachable rear end head I@ secured. to the casing body as by screws and an integral front head i5 provided with a detachable front plate i6 secured to the front head likewise as by screws. The supporting handle 3 is arranged along the upper side of the casing body between the end heads ill and I5, and includes a longitudinal bolt Il (Fig. 5) secured to the heads and surrounded by a sleeve I8, about the outer surface of which a rubberlike grip i9 is attached. The handles ll, l project laterally in alignment from the opposite sides of the rear head lli and are similarly provided with rubberlike grips 2i). Thus the drill may be readily transported, and supported with respect to the work during drilling, with comparative ease. The casing contains the motor 5.

Now referring to the rotating mechanism 8 for the drilling implement, it will be noted that xed to the front end of the motor shaft 2| is a spur pinion 22 meshing with a spur gear 23 which has formed integral therewith a coaxial spur gear 24. The gears 23 and 2l! are journaled on a shaft 25 supported within the casing head l 5 and suitably xed to the front plate i5. The gear 2l!- meshes with and drives a large spur gear 25 which has formed integral therewith a coaxial spur gear 21. The gears 25 and 2l are journaled on a shaft 23, likewise `supported within the front casing head and fixed to the front plate. The gear 21 meshes with and drives a large spur gear 29 keyed at 3|) to a hollow shaft or sleeve 3| journaled in bearings 32 and 33 respectively supported by the casing-body and the front head. Arranged within the shaft 3| and splined thereto at 54 is a reciprocable shaft member 35. Threadedly secured at 36 to the front end of the splined shaft is a coupling member 31 providing a threaded socket for receiving the threaded shank 38 of the drilling implement. Thus, when the motor 5 is running, the drilling implement is rapidly rotated to effect its rotary boring function through the gearing above described.

The impact mechanism 5 comprises a bevel pinion 48 fixed to the rear end of the motor shaft 2| and meshing with and driving a bevel gear li having its hub i2 keyed to a transverse shaft i3 journaled within bearings and l5 suitably supported within the rear head lli. The inner end of the shaft d3 is formed with a crank arm 4&5 carrying a crank pin 41|. Arranged in the bore of the shaft 43 in coaxial relation with the shaft is a relatively rotatable shaft diri held against axial displacement from the shaft bore by a screw 49 projecting into an annular groove 5! on the reduced inner end of the shaft i3 as shown in Fig. 5. The outer end of the shaft i3 is formed with a crank arm 5i carrying a crank pin 52 to which the rear end of a connecting rod or link 53 is pivotally attached at 51.5. The front end of the link 53 is longitudinally slotted at 55, and passing through this `slot is a transverse pin 5S secured at its ends within the rearward portion of a reciprocable impact element 5l. This impact element has a cylindrical body 5S formed with a small axial passage 58 and provided with an enlarged circular forward portion or flange 59 tapering to a forward impact surface fili. The passage 58' acts as a pressure relief to prevent excessive air pressures from building up in .ad- Vance of the piston.v The front circular portion or flange 5S is reciprocably guided in a sleeve 6|, and the body 58 is reciprocably guided in a sleeve 62. The sleeve is arranged in a longitudinal bore 55 in the casing body and is seated at its forward end against a shoulder M, and the sleeve 52 is formed with a flange 55 clamped between the rear end of the sleeve 5| and the rear head I4, as illustrated. Encircling the sleeve 52 and the body of the impact element is a powerful coil spring 55 which acts between the fiange 59 and the flange 55 to urge the impact element in a forward direction. The splined shaft member 35 has a rearward enlargement 6l formed with a rear surface (i3 which receives the impact blows of the impact element 5l. The hollow shaft or sleeve 3| is formed with a rearward enlargement 69, and secured between the enlargement 61 and |59 and surrounding the rearward portion of the shaft 35 is suitable resilient means, herein a mass lil of resilient material desirably composed of a rubberlike substance such as neoprene, which, due to its inherent resiliency, urges the splined shaft 35 toward its rearmost position with the coupling member 3'! against the front end of the splined shaft 35, as shown in Fig. 5. There is clearance at il between the inner surface of the resilient mass ill and the shaft member 35, which permits the to expand inwardly, as well as outwardly, when under substantial compression, to obtain the desired resilience. As the shaft 43 is rotated by the motor 5 through the bevel gearing, the crank arm 45 is turned about the axis of the shaft 53 to bring the crank pin l1 against one side of the crank arm 5| (see Fig. ll), to cause the crank arm 5| to turn with the shaft d3 about the axis of the shaft 48 (see also Fig. l2) thereby to draw the impact element 5i rearwardly against the action of the spring 55, compressing the latter to a predetermined high degree. Before the crank pin 41 assumes its rearmost position, as shown in Fig, 13, the crank arm 5| passes dead center and then leaves the crank pin 41, pennittlng the `highly compressed spring 66 to drive lthe impact element 51 forwardly with great speed to deliver a powerful blow to the 'impact .surface 58 of the splined shaft 35. Since the drilling implement is fixed to the shaft 35, the blow of the impact Telement is transmitted therethrough to the drill bit l. A rapid series of blows are delivered to the impact surface of the shaft 85 during the drilling operation to a'ctuate the drill bit l'to perform a percussive cutting action, Vand this percussive action supplements the rotary boring action, thereby resulting in increased drilling speed.

The conveying means I0, associa-ted with 'the drilling implement, comprises an elongated "cylindrical tube 'l2 secured atits rear end as by'a split clamp and bolt 'l5 in a bore T4 in a forward 1'ex tension the front head plate l5. This tube is adapted to extend into 'the drill hole in the manner shown in Fig. l, and its outer end has fixed, as by bonding to its exterior, a resilient sleeve 'it preferably composed of a rubberlike material. This sleeve is folded `back on 4itself at T1 to provide a circular yieldable wall 'F8 sealingly engaging the walls of the Adrill hole.

Formed on the exterior of the drilling implement 6 are spiral vanes 7S which provide a spiral conveyor for moving the cuttings rearwardly from the drill bit through the tube l2. Thus thecut tings created by the drill bit during the drillingr operation are moved rearwardly' through the tube and are discharged at the rear end of the spiral conveyor into a chamber 30 .in the front plate extension l5. The chamber 30 has a bottom discharge opening 8| through which the cuttings s are discharged by gravity from the chamber. The coupling member 3l has a radial flange running at periphery close to Vthe walls of the chamber Si? to keep the cuttings from packing inwardly toward thefront bearing 33.

Now referring to the improved :cooling means l, it will be noted that the motor 5 'is of the air cooled type, and has a cooling fan 84 fixed to its power shaft and contained in a cross chamber 85 at the forward end of the motor. Extending ylongitudinally along opposite sides of the casing body are parallel flow passages 86, B6 which communicate at their front ends with the front chamber Sii and at their rear ends with side pockets El connected by a cross chamber 88 at when the 4otor 5 is running, cooling iiuid such as coolin., fr is circulated in a closed circuit or path axially through the motor casing, then laterally through the iront chamber 85, longitudinally rearwardly through the passages '85, and thence through the pockets di! and the rear chamber 88 of 'the motor, to reduce the operating temperature of the latter.

In order conveniently to operate the switch 89, one of the grips 20 of the handles 4, 4 is rotatably mounted and has a lateral arm. 98 pivotally connected by a link 91 to one end of a lever 98 pivoted at 99 on a bracket `llll integral with the casing body. The lever 98 at its other 'end is pivotally connected at |D| to a splined .rod |02 suitably guided in the casing and operatively connected `to the switch actuator. This operating rod is urged outwardly toward open-switch .position by a spring |93. By such arrangement, 'the 'switch may be readily controlled by the operator 6 without release of his grip on the supporting handles 4, 4.

The modified embodiment relates to the invention from its percussive aspect, and, as shown in Figs. 14 to 19 inclusive, comprises a percussive tool preferably for drilling shallow holes in concrete or similar materials, and, in this construction, the rotating mechanism for the drilling irnplement of the preferred illustrative embodiment is omitted. In this instance, there is a casing having secured thereto at Hl at its rearward `end a handle |01 for supporting and positioning the tool. Attached as by screws to one `side of the casing is a iianged member ldd formed with a sleevelike, split clamp portion |99 for receiving v'and supporting a cylindrical portion |10 of a motor lil, herein an electric motor. Fixed to the motor shaft i l2 is a curved arm or crank l which is engageable with an elongated crank pin |14 secured to e, crank arm or disk l l5. This crank disk has a shaft portion iii in arial alignment with the motor shaft and suitably journaled in bearings supported within a tubular bearing support ill' integral with the casing. Pivotally connected to the crank lin a connectu ing rod or link H8, in turn pivotally connected through a pin H9 and a slot l2@ to a guide ele ment |2|. This guide element is reciprocably guided in a bore |22 in a tubular portion |23 of the casing and has threadedly attached thereto, at |24, a forwardly extending rod |25 which is threadedly connected at |26 at its forward end to an impact element |2l1 (see Fig. 16). The impact element 421| is reoiprooably guided in a bore |23 of a tubular casing portion |29 which is arranged in axial alignment with the casing portion |23, and is coupled thereto as by a coupling sleeve it. Loosely positioned within this lcoupling sleeve |39 between the adjacent ends of the casing portions |23 and ld is a guide meinber |3| for guiding the rearward portion of the recprooable rod |25. A coil spring $32 is arranged between the front end of the guide meniber |3| and the rear end of the impact element |27 for urging the latter forwardly. Threaded at |33 to the front end of the casing portion Ii is .a front can i3d having a hexagonal bore or socket |735 for receiving the hexagonal shank i3d of a drilling implement i3?. A tappet or striking block ld is also guided in the casing bore |23 and has a socket |38 for receiving the rearward portion of the shank of the drilling imple ment. A suitable securing device, such as a set screw 39, serves to secure the tappet rigidly to the shank. Arranged between the 'front cap |313 and 'the tappet |33 and surrounding the shank |36 is a coil cushion spring ifll for urging the tappet rearwardly. A collar idi, fixed to the shank |35. limits movement of the shank in a rearward direction within the cap-bore i 35. The drilling implement has an integral drill bit |42 at its forward end. as shown.

Durii operation oi the tool of the modified illustra v Trient above described, the operator gra-eps the handle iil'l and the forward body portion me of the tool casing, and when the tool is properly positioned with respect to the worls, the motor iii be suitably started. causing the curved arm or crank H3 to turn about the motor axis. When this arm engages the pin id (see Fig. .17), the crank ein is turned rearwardly as shown in Fig. i9. before, the arm assumes the position shown Fig. A18, the vcrank pin ill leaves thearni, and the spring |32 moves the impact element I2? rapidly When, or justV a forwardly to cause the latter to strike a powerful blow on the tappet |38 which transmits the blow to the shank of the working implement. During drillingJ the operator may bodily rotate the tool about its longitudinal axis, thereby to oscillate the drill bit 42 about its axis to change the position of the cutting edges of the bit as the latter is percussively actuated.

In both embodiments of the invention above described, the pin and slot connection between the connecting rod and the impact element permits the latter to strike its blow without transmission of undue shocks to the connecting rod and the crank pin. Also, this pin and slot connection permits the impact element to move on rebound after it strikes its blow freely rearwardly relative to the connecting rod without shock to the latter. The preferred `enfibodiment of the percussive mechanism illustrated in Figs. l to i3 inclusive may be employed without automatic rotation mechanism, and in the modified embodiment, rotation mechanism for the drilling implement may be provided if desired.

As a result of this invention, an improved drilling apparatus is provided having improved impact mechanism whereby the drilling implement is percussively actuated in a novel manner. It will further be evident that by associating the impact mechanism with the rotating mechanism for the drilling implement, the drilling implement is percussively actuated as it is rapidly rotated so that a percussive drilling action supplemcnts the rotary boring action to increase the drilling speed. It will further be evident that by the provision of the motor driven crank which 2 engages the crank pin or crank arm for ccmpressing the spring, the latter is suddenly released at its point of maximum compression so that the impact element is driven rapidly forwardly to impart a powerful blow to the drilling implement. The drilling apparatus is rugged in construction and simple in design. Other advantages of the invention will be clearly apparent to those skilled in the art.

While there are in this application specifically described two forms which the invention, in at least one of its aspects, may assume in practice, it will be understood that these forms of the same are shown for purposes of illustration, and that the invention may be modified and embodied in various other forms without departing from its spirit or the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent is:

l. In a drilling apparatus, the combination comprising a reciprocable impact element, resilient means for urging said impact element in one direction, and motor driven mechanism for moving said impact element in the opposite direction against the action of said resilient means including relatively movable crank arms turnable about axes in the same straight line, a motor for turning one crank arm, means for operatively connecting said other crank arm to said impact element, said one arm upon turning thereof engaging said other arm to turn the latter at the same angular rate therewith thereby to move said imp-act element in a direction to effect compression of said resilient means, and said other arm when said resilient means attains a predetermined maximum compression being re- 2. In a drilling apparatus, the combination comprising an impact element adapted to deliver a rapid series of blows to a drilling implement, compressible resilient means which when released drives said impact element forwardly to effect delivery of a blow to said drilling implement, and motor driven mechanism for actuating said impact element to effect compression of said resilient means including coaxial relatively rotatable shafts, a motor for driving one of said shafts, operative connections between said other shaft and said impact element, and means on said one shaft for rotating said other shaft at the same angular rate therewith and from which automatic release is effected at a predetermined position thereof to permit free rotation of said other shaft relative to said motor driven shaft to permit said resilient means to drive said impact element forwardly to strike its blow.

3. In a drilling apparatus, the combination comprising an impact element adapted to deliver a rapid series of blows to a drilling implement, compressible resilient means which when released drives said impact element forwardly to effect delivery of a blow to said drilling implement, and motor driven mechanism for actuating said impact element to effect compression of said resilient means including coaxial relatively rotatable shafts, a motor for driving one of said shafts, operative connections between said other shaft and said impact element including a crank arm, and means including a crank pin on said one shaft for rotating said other shaft at the same angular rate therewith and from which automatic release is effected at a predetermined position thereof to permit free rotation of said other shaft relative to said motor driven shaft to permit said resilient means to drive said impact element forwardly to strike its blow.

4. In a drilling apparatus, the combination comprising a reciprocable impact element adapted percussively to actuate a drilling implement, a spring for urging said impact element in a forward direction, and motor driven mechanism for moving said impact element rearwardly against the action of said spring and embodying means for automatically releasing said impact element when said spring attains a predetermined compression including a crank arm, a relatively movable. crank arm disposed in the path of movement of said rst crank arm and carrying a crank pm, a connecting rod connecting said crank pin to said impact element, said first crank arm upon turning'thereof engaging the rear surfacel of said second crank arm to turn theI latter at the same angular rate therewith and said second crank arm when said arms attain a predetermined relation turning freely away from said rst crank arm to permit said spring to drive said impact element forwardly to strike its blow.

5. In a drilling apparatus, the combination comprising a reciprocable impact element, a motor having a rotating power shaft, and mechanism for effecting reciprocation of said impact element including compressible resilient means for urging said impact element in one direction, a crank arm driven by said motor and having a crank pin, a second crank arm coaxial with said rst crank arm and rotatable relative thereto. and operative connections between said second crank arm and said impact element, said first crank arm upon turning thereof having its crank pin engage said second crank arm for turning the latter at the same angular rate therewith to effect compression of said resilient means, and said second crank arm when said arms attain a predetermined relative position turning freely rela.- tive to said first crank arm to permit said resilient means to effect rapid movement of said impact element to cause the latter to deliver its blow.

6. In a drilling apparatus, the combination comprising a reciprocable impact element, a motor having rotating power shaft, and mechanism for effecting reciprocation of said impact element including c-ompressible resilient means which when released drives said impact element forwardly to effect delivery of a blow, a. crank arm driven by said motor and having a crank pin, a second crank arm coaxial with said rst crank arm and rotatable relative thereto and operative connections between said second crank arm and said impact element including a connecting link having a. longitudinal slot and a pin passing through said slot and secured to said impact element, said first crank arm upon turning thereof having its crank pin engaging said second crank arm for turning the latter at the same angular rate therewith to effect compression of said resilient means, and Said second crank arm when said arms attain a predetermined relative position turning freely relative to said first crank arm to permit said resilient means to effect rapid movement of said impact element to cause the latter to deliver its blow, said pin and slot connection when said impact element strikes its blow reducing the transmission of shock to said reciprocating mechanism.

7. In a drilling apparatus, the combination comprising a reciprocable impact element, a motor having a rotating power shaft, and mechamsm for effecting reciprocation of said impact element including compressible resilient means which when released drives said impact element forwardly to effect delivery of a blow, a curved crank arm driven by said motor power shaft, a coaxial crank arm having an elongated crank pin and operative connections between said crank pin and said impact element, said first crank arm upon turning thereof engaging said crank pin for turning said second crank arm at the same angular rate therewith to effect compression of said resilient means, and said second crank arm when said arms attain a. predetermined relation turning freely relative to said first crank arm to permit said resilient means to effect movement of said impact element in a direction to cause the latter to deliver its blow.

8. In a drilling apparatus, the combination comprising an impact element adapted to deliver a rapid series of blows to a drilling implement, compressible resilient means which when released drives said impact element forwardly to effect delivery of a. blow to said drilling implement, and motor driven mechanism for actuating said impact element to effect compression of said resilient means to a predetermined degree including coaxial relatively rotatable shafts, the outer one of said shafts having an axial bore into which said other shaft extends and in which said latter shaft is journaled, a motor for driving one of said shafts, operative connections between said other shaft and said impact element,

and means on said one shaft for rotating said other shaft therewith and from which automatic release is effected at a predetermined position thereof to permit free rotation of said other shaft relative to said motor driven shaft to permit said resilient means to drive said impact element forwardly to strike its blow.

9. In a drilling apparatus, the combination comprising an impact element adapted to deliver a rapid series of blows to a drilling implement, compressible resilient means which when released drives said impact element forwardly to effect delivery of a blow to said drilling implement, and motor driven mechanism for actuating said impact element tol effect compression of said resilient means to. a predetermined degree including coaxial relatively rotatable shafts, said shafts projecting in opposite directions, a motor for driving one of said shafts, operative connections between said other shaft and said impact element, and means on the inner end of said one shaft for enga-ging the adjacent end of said other shaft for rotating said other shaft therewith and from which automatic release is effected at a predetermined position thereof to permit free rotation of said other shaft relative to said motor driven shaft to permit said resilient means to drive said impact element forwardly to strike its blo-w.

10. In a drilling apparatus, the combination comprising a reciprocable impact element, resilient means for urging said impact element in one direction, and motor driven mechanism for moving said impact element in the opposite direction aga-inst the action of said resilient means including relatively movable drive members having bearing portions arranged in axial alignment, one member disposed in the path of movement of the other, a motor for driving said other drive member, means for operatively connecting said one drive member to said impact element, said other drive member upon driving thereof by said motor abutting said one drive member to move the latter in unison therewith, thereby to move said impact element in a direction to effect compression of said resilient means, and said one drive member when said resilent means attains a predetermined maximum compression moving freely away from said other drive member to effect release of said resilient means/tol permit the latter to drive said impact element rapidly in the direction to deliver a blow.

JOSEPH F. JOY.

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